Thickness control apparatus for rolling mill

ABSTRACT

A thickness control apparatus for multi-stand rolling mills wherein the thickness instruction is changed during rolling. When the rolling material reaches a stand at which the change of the thickness of the rolling material is to be effected, the gap or opening of the stand is changed, and at the same time, the roll speed of the previous stand is changed, whereby the tension of the rolling material between both of the stands is made equal to the tension in the schedule before changing the thickness.

United States Patent 1 Kitanosono et al.

1451 Oct. 2, 1973 THICKNESS CONTROL APPARATUS FOR ROLLING MILL [75] Inventors: l-lidehiro Kitan0sono;TakeakiKubo,

Arimura et al. 72/8 Masterson, Jr. 72/8 Primary ExaminerMilton S. Mchr Attorney-Craig, Antonelli, Stewart & Hill [57 ABSTRACT A thickness control apparatus for multi-stand rolling [30] Forelgn Apphcatlon Pnonty Data mills wherein the thickness instruction is changed dur- Mar. 9, 1970 Japan 45/19344 ing toning w the rolling material reaches a stand at which the change of the thickness of the rolling ma- [52] U.S. Cl. 72/11, 72/24() teria] is to be effected, the gap or Opening of the Stand [51] Int. Cl BZIb 37/00, B2lb 37/l4 is changed, and at the Same time, the roll Speed of the [58] Field Of Search 72/6-12, previous and i changed whereby the ension of the 72/16 rolling material between both of the stands is made equal to the tension in the schedule before changing [56] References Cited the thickmss UNITED STATES PATENTS 3,618,348 11/1971 Arimura et al. .l 72/7 11 Claims, 11 Drawing Figures FIRST STAND SECOND THII E J STAND ROLLING hz O l MATERIAL a s ROLLING DIRECTION l l a Pmmmw'w I 3.762.195

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FIG. 2a :5

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B A FlG.2e f AM B A FlG.2f Cm I NVENTORS HI DEHIR O KITANOSONO BY TAKEAKI Kuao Craig, AnlBneUi, Skmk Hill ATTORNEYS PATENTEUUBT-ZIHB 3.762.195

SHEET anr 4 FIG. 3b

DET M INVENTOR5 H oemno KITANOSONL BY TAKEARI KU BO Craig, Anl oneui, Stewart ATTORN Y THICKNESS CONTROL APPARATUS FOR ROLLING MILL BACKGROUND OF THE INVENTION The present invention relates to a gauge control device in a rolling mill for obtaining rolled material having different gauges from a single rolling material.

Generally, a single material is rolled to have one uniform gauge rather than being rolled into rolled materials having two or more gauges or plate thickness.

With such a gauge control apparatus for rolling material, in order to obtain rolled material having different gauges, ithas generally been the practice to install several sets of similar apparatus, one for each gauge, or to stop temporarily the rolling to change the schedule of the rolling (effect alteration of the roll gap, etc.) and after which to commence the rolling using a new rolling material. The former has the disadvantage that the cost of equipment increases greatly, and in the latter case, there is the unavoidable drawback that the rolling efficiency becomes extremely low.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gauge control apparatus which makes its possible to achieve a rolling having two or more different gauges which can be obtained quickly from a single rolling material, and also which reduces the off-gauge portion of the plate thickness where the gauge is to be altered.

It is to be noted that a single rolling material is meant to include one which can be considered as comprising several materials connected.

The characteristic feature of the present invention is, in a rolling mill comprising a plurality of rolling stands which are to obtain rolled materials of more than two different gauges from a single rolling material, that the roll gaps of the stands are altered and controlled so as to obtain a gauge of the new schedule instead of the gauge of the preceding schedule each time an altering point of the gauge (predetermined position of the rolling material, the gauge of which is to be altered) reaches the rolling stand, and to control the tension so that the variation of tension, which might be produced by the variation of each of the roll gaps, will not affect the delivery gauge of each of the stands.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram explaining the principles of the present invention;

FIG. 2a-2f are views showing the forms of rolling material at each of the points where the gauges are altered;

FIGS. 3a-3c show an embodiment of the present invention; and

FIG. 4 shows the relation of arrangement between each of FIGS. Zia-3c.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, an explanation will be given of the problems relating to the control of the rolling of material and the solution of these problems in accordance with the present invention, considering a case wherein two different gauges of material are to be obtained by a multi-stand (three-stand) rolling mill, as shown in FIG. 1.

The symbol A designates a point of alteration or transition of the gauge at which the gauge is to be altered. Since the alteration of the gauge must necessarily be carried out during an altering period wherein the roll gap is adjusted to achieve the alteration of the gauge as the rolling material advances, the new gauge is not accomplished until a point B is reached which is slightly behind the point A. The present invention does not intend to eliminate this off-gauge portion between the point A and the point B, but serves to control the rolling operation so that effects of gauge alteration between the points A and B will not disturb the stand which is already effecting a rolling according to the new schedule and the stand which is still effecting a rolling according to the preceding schedule.

In FIG. 1, the first stand changes its gap from S to a new schedule of S, at an instant when the gauge alteration point A reaches the first stand. In this case, since the delivery gauge of the first stand is changed between the first and the second stands, the tension is changed. With this change of tension between the first and the second stands, the tension between the second and the third stands is also changed.

This change in tension will not give the expected value of gauge for the rolling material which is bitten in the rolling mill, and when the variation of tension is severe, it may cause damage, such as breaking of the rolling material. Practically, it is the tension per unit area, that is to say, the unit tension which affects the gauge. The unit tension can generally be calculated easily from the following equation if the total tension between the rolling stands is known.

t T lh b (i+l)e ry/ on) b where t delivery unit tension at the i stand,

T total tension between the i stand and the (i+l) stand,

h delivery gauge at the i stand,

h feeding gauge at the (i+l) stand b: breadth of the plate (breadth of the rolling material) t feeding unit tension at the (i+l) stand.

As is clear from the equations (1) and (2), in the case of ordinary rolling (the case in which one kind of rolled material is rolled from a single rolling material), the delivery unit tension t of the i stand is, in general, exactly equal to the feeding unit tension of the following (i+l) stand. This is because the relation h, h is realized. The total tension T between the i stand and the (i+l) stand can be calculated from the following equation:

U I ania l+m in u- 1 d! where:

b: breadth of the plate V speed at the neutral point of the (i+l stand, h z gauge at the neutral point of the (i+l stand, V speed at the neutral point of the i stand, h gauge at the neutral point of the i stand.

When the altering point A of the gauge reaches the i stand and the gauge alteration is effected at the i stand, the feeding unit tension t at the (i+1) stand which is rolling with the preceding schedule, with the i stand as the boundary, is changed due to the change in total tension T between the i stand and the (i+l) stand due to the gauge alteration of the i stand. in order to prevent the change in t from affecting the other stands, it is necessary to control the rolling so that the total tension T between the i stand and the (i+l) stand is always constant. Also, since the total tension T between the (i-l stand and the i stand is also changed, the tension T must also be controlled so that there is no change therein.

First, to maintain the total tension between the i stand and the (i+l) stand constant, it is necessary from the above equation (3) that A it u+m uum in m} At From this equation (4), the following equation becomes the condition for maintaining the total tension T constant. Similarly, the condition for maintaining the total tension E constant is as follows:

in m U-lln u-m Now, when the gauge altering point A reaches the first stand in FIG. 1, and the alteration of the roll gap begins at the first stand, the total tension T between the first and the second stands is liable to be changed, so that this must be prevented. This is effected, for example, by varying the roll speed of the first stand. In this case, it can be effected easily by using the equation (5). Namely, the equation in 21 ilt/ m where:

V speed at the neutral point of the first stand, V speed at the neutral point of the second stand, h gauge at the neutral point of the first stand,

it gauge at the neutral point of the second stand, can be used.

When beginning alteration of the roll gap of the first stand, the gauge k at the neutral point of the first stand begins to change. Accompanied thereby, the speed at the neutral point in the first stand is varied so that the speed becomes V given by the equation (6). What is important for this control operation is the method of finding the gauge at the neutral point (hereinafter referred to as neutral gauge) and the speed at the neutral point (hereinafter referred to as neutral speed"). There are various known methods 'of finding the neutral gauge; an example is shown in the following where: d M/tan (oz/2) H: feeding gauge of the roll mill, in: delivery gauge of the first stand, M: coefficient of friction,

a: bite angle.

Also, the neutral speed is equal to the roll speed. Accordingly, by finding the neutral gauge with the equation (7) and by measuring the roll speeds of each of the stands, the roll speed of the first stand can be controlled by the equation (6).

With this control, the total tension T between the first and the second stands are maintained always constant, and the feeding unit tension of the second stand does not change until the point A, at which the gauge is to be altered, reaches the second stand. Since the feeding unit tension 1 of the second stand does not change, no effect on the tension is exerted at all on the succeeding stands (in this case, the third stand), and the delivery gauges I1 and h at each stand remain at the desired values of the original schedule. However, the problem which must be considered is that the delivery unit tension i of the first stand is changed by the change of delivery gauge of the first stand. Due to the change in this unit tension 1, and the roll speed V of the first stand (on condition that V,,, V,), the delivery gauge of the first stand does not turn out to be the desired gauge h, of the new schedule (after the gauge is altered), so that it is necesary to consider all of these factors before setting the roll gap in accordance with a new schedule.

When the point A, at which the gauge is to be altered, reaches the second stand, and the alteration of the roll gap to the new schedule begins at the second stand, the total tension T between the second and the third stands varies, so that it is necessary to vary the roll speed at the second stand. Determining the roll speed at the second stand by the equation (5), and controlling it thereby, the total tension T between the second and the third stands does not change, so that the gauge will not be affected. In practice, however, there appears a variation in tension with such a control operation. This is because the ratio of speeds of each roll at the first and the second stands, which has up to that time been balanced when the point A, at which the gauge is to be altered, reaches the second stand, is disturbed due to the variation in the roll speed of the second stand, and thus the total tension T between the first and the second stands changes again. To prevent this variation, after the point A, at which the gauge is to be altered, reaches the second stand, and the alteration of the gauge at the second stand has commenced, the roll speed of the first stand should be altered while maintaining a certain speed ratio with the roll speed of the second stand.

This means that the equation (4) is always satisfied. In this way, the delivery gauge at the first stand maintains the newly required gauge b and the total tension T between the second and the third stands does not change, so that the delivery gauge at the third stand is controlled to the previously desired gauge h (before alteration of the gauge). When the point A, at which the gauge is to be altered, reaches the third stand, the roll gap at the third stand is varied so that the gauge h of the new schedule is obtained. In FIG. 1, since a three-stand rolling mill is considered, all the stands are set so that the gauge required by the new schedule is obtained at the stage where the alteration of the roll gap of the third stand is finished.

FIGS. 2a through 2f show the gauges of the rolling material at each point of the control operation. In the drawing, FIG. 2a shows the material at the instant when the point A, at which the gauge is to be altered, reaches the first stand. From this instant on, the alteration of the roll gap and the accompanying alteration of roll Lspeed are commenced at the first stand, and thisis shown in FIG. 2b. FIG. 2c shows the instant at which the alteration of the roll gap and the roll speed at the first stand is finished.

From this instant on, the delivery gauge of the first stand becomes the desired gauge 11, of the new schedule, that of the second stand becomes the desired gauge h of the previous schedule (after the second stand, it is controlled by the previous schedule), and this is shown in FIG. 2d. FIG. 2e shows the instant where the point A, at which the gauge is to be altered, reaches the second stand, and where the alteration of the roll gap has commenced, and it is so controlled by varying the roll speeds of the second and the first stand that the delivery gauge of the first stand becomes the desired gauge h, of the new schedule, and the delivery gauge (not shown) of the third stand becomes the desired gauge h of the previous schedule. FIG. 2f shows the instant at which the alteration of the roll gap in the second stand is finished. By controlling the rolling in this way, there is obtained a rolled material having different gauges on both sides of the range defined by the point A, at which the gauge is to be altered, and the point B, at which the alteration of the gauge is finished.

The invention will now be described with reference to a specific example. FIGS. 30 through 3c, when combined as shown in FIG. 4, illustrate an embodiment of the present invention. In this example, the apparatus according to the present invention is practiced on a multi-stand (five-stand) rolling mill.

Each of the stands is controlled in accordance with a rolling schedule, and the gauge of the rolling material is altered during the rolling operation while the rolling is continued. When the altering point A of the gauge (predetermined point of the rolling material at which the gauge is to be altered) reaches the first stand, the roll gap of the first stand is altered so that the delivery gauge at the first stand has a new schedule. In this case, the roll gap is caused to vary by controlling the tension, while appropriately taking notice that the alteration of the roll gap of the first stand is a transient one and at the same time that the unit tension at the new gauge is different from that of the schedule before the gauge is altered. It is so constituted that whenever the second through the fifth stands bite the altering point A of the rolling material, the roll gap of the stand to which the altering point A has been bitten and the roll speed of the previous stand including the stand are altered.

Referring now to the apparatus shown in FIGS. 3a through 3c, the numeral 1 designates the first stand, 2 is the second stand, 3 is the third, 4 is the fourth stand, 5 is the fifth stand, 11-15 are driving devices for adjusting the roll gap for each of the stands (screw-down motors), 21-25 are screw-down devices associated with the rolls for each of the stands, 31-35 are detectors of the roll gap for each of the stands, 41-45 are driving devices associated with the roll for each of the stands, 51-55 are speed detectors associated with the roll for each of the stands, 61-65 are detectors of the rolling load for each of the stands, 71-75 are gauge calculators for each of the stands (h S PIM), 81-85 are detecting devices for detecting the gauge altering point to ensure that the rolling proceeds after the rolling material is bitten and that the altering point of the gauge is reached for each of the stands, and to generate signals in response thereto, is an instructing device for generating signals defining the rolling schedule which determines the roll speed and the set value of the delivery gauge for each of the stands, 101-105 are gate circuits for opening gates in response to the instruction for altering the gauges, is a roll gap calculator for calculating the controlling roll gap to obtain the gauges from the delivery gauge of each stand from the rolling schedule instructing device 90 and to supply it to the roll gap driving device (ll-l5), 121-125 are thickness calculators for calculating the neutral gauges of each stand, 131-134 are calculators for control of roll speed which calculate the control required for the roll speed of the first to the fourth stands.

The operation of this embodiment will be explained.

The schedule of the rolling, that is, the desired gauge and the desired speed has all been calculated by the rolling schedule instructing device 90, which is a conventional device provided in the rolling mill to control the rolling operation. Accordingly, first the roll gaps and the roll speeds from the first stand to the fifth stand are established. When the rolling begins and the tip end of the rolling material reaches the first stand, the detecting device 81 for detecting the altering point of the gauge at the first stand confirms that the rolling material has reached the first stand by the change in output of the rolling load detector 61 of the first stand, and from that time on, in response to the output V, of the roll speed detector 51 of the first stand, begins to integrate V with time t. Namely, using an operation expressed by an equation I I V dt, which equals the length of the rolling material passing through the first stand, and when the length l becomes equal to the predetermined length I, that is to say, when the gauge altering point A reaches the first stand, the detecting device 81 for the gauge altering point generates a signal. By the output signal of the detecting device 81 for the gauge altering point at the first stand, the gate in the gate circuit 101 is opened, the new schedule delivery gauge h, of the first stand is received in the calculator 110 for the roll gap, which is a typical servo control arrangement, the calculator 110 for the roll gap calculates the control m, of the screw-down driving device 11 for varying the roll gap of the first stand from the previous schedule S to the roll gap 8, calculated by the gauge h, in the new schedule, and forwards the control m, to the screw-down driving device 11. As a result, the screw-down device 21, and the roll gap of the first stand is altered from S, to S A definite time is required for this alteration, and when the alteration of the roll gap begins, the delivery gauge of the rolling material passing through the first stand is settled from that of the previous schedule h, to the delivery gauge h, of the new schedule.

In order to eliminate the effect due to the change in gauge upon the other stands, the roll speed of the first stand is varied so that the total tension T between the first stand and the second stand is not changed. To determine the quantity of variation of the roll speed, the

gauge h, of the first stand and the gauge h: of the second stand is determined by the gauge calculator 71 of the first stand and the gauge calculator 72 of the second stand. The gauge h, is supplied to the neutral gauge calculator 121 of the first stand, and the gauge I1 to the neutral gauge calculator 122 of the second stand, which calculate the neutral gauge k of the first stand and the neutral gauge h, of the second stand using the equation (7), and the roll speed of the second stand (which is equal to the neutral speed V is detected by the roll speed detector 52 of the second stand. The neutral gauges 11 and h and the roll speed V, of the second stand are supplied to the calculator 131 for the roll speed of the first stand, which calculates the control quantity V for the roll speed of the first stand from the above-described equation At this stage, the first stand gauge calculator 71 receives the output of the roll gap detector 31 of the first stand and the output of the screw-down detector 61 of the first stand, respectively, and calculates the (delivery) gauge h of the first stand using a generally known related formula. The other gauge calculators 72, 73, 74 and 75 are also adapted to determine each of the gauges in a simlar manner.

In this way, when the control V, for the roll speed at the first stand is found, the roll driving device 41 of the first stand effects a correction of the roll speed by V,', and the control is continuously effected at the first stand so that the total tension T between the first and the second stands is not changed. As described before, from the instant when the gauge altering point A of the rolling material reaches the first stand, an output signal is generated by the detecting device 81 for the gauge alteration of the first stand, and at the same time said signal is generated, the detecting device 82 for gauge alteration of the second stand receives the output V of the roll speed detector 52 of the second stand by said signal, which begins to integrate with time I. When the integrated value becomes equal to the distance between the first stand and the second stand, that is, when the gauge altering point A reaches the second stand, the detecting device 82 begins to generate an output signal.

Also, the detecting devices 83, 84 and 85 for detecting the gauge altering point at the third stand, the fourth stand and the fifth stand receive the stand roll speed by the output signal of the alteration detecting device of the preceding stand similar to the detecting device 82 for the gauge altering point of the second stand, and begin to deliver the output signal at the instant when the gauge altering point A reaches the corresponding stand.

Until the gauge altering point A reaches the first stand, the gauge alteration at the first stand is completed, and the altering point A reaches the second stand, the roll speed of the first stand is controlled so that the total tension T between the first stand and the second stand is maintained constant. When the gauge altering point A reaches the second stand, and the output signal is generated from the detecting device 82 for detecting the gauge altering point at the second stand, the gate of the gate circuit 102 is opened, and the delivery gauge h, of the second stand according to the new schedule is received by the calculator 110 for determining the roll gap. By this calculator 110, the new control of the roll gap m of the second stand is calculated, and it is supplied to the driving device 12 for adjusting the roll gap. The driving device 12 operates the screw-down device 22 by m and the roll gap is altered to the new roll gap 8,. In order to eliminate the effect of alteration of this roll gap (at and after the alteration), the gauge h at the second stand and the gauge h at the third stand are obtained from the gauge calculators 72 and 73, which supply signals h and h to each of the neutral gauge calculators 122 and 123, thereby calculating the neutral gauge k of the second stand and the neutral gauge h of the third stand, and also detecting the roll speed V of the third stand from the roll speed detector 53 and supplying the signals h h and V to the calculator 132 for the roll speed of the third stand to calculate the control V for roll speed of the second stand. By the output V, of the calculator 132 for roll speed, the roll driving device 42 of the second stand corrects the roll speed so that the total tension T between the second and the third stand will not be changed.

In case the roll speed of the second stand is changed, the total tension T between the first stand and the second stand is changed unless the roll speed of the first stand, which has a certain relation with the roll speed of the second stand, is also changed. However, the roll speed of the first stand, which is controlled by detecting the gauge h, at the first stand, gauge 11 at the second stand and the speed V of the second stand for maintaining said total tension T constant, is controlled so that the total tension T between the first stand and the second stand is maintained constant corresponding to the variations in said inputs h 11 and V automatically. Therefore, the rolling material is not influenced at all by the variation of roll speed at the second stand.

When the gauge alteration (alteration of the roll gap) at the second stand is terminated, and the gauge altering point A reaches the third stand, the detecting device 83 for detecting the gauge altering point of the third stand begins to generate an output signal. By this signal, the gate in the gate circuit 103 is opened, and the delivery gauge h of the third stand is supplied to the calculator for determining the roll gap.

The control m of this calculator for the roll gap is supplied to the roll gap driving device 13 of the third stand, the screw-down device 23 is operated, and the roll gap is altered to the new roll gap 5;. In order to eliminate the effect at and after the alteration of the roll gap of the third stand, the gauge h of the third stand and the gauge h of the fourth stand are supplied to each of the neutral gauge calculators 123 and 124 from the gauge calculators 73 and 74, and they calculate the neutral gauges 11 and h.,,,, and also the control V for roll speed of the third stand is found from the values of 11 and h and the output V, of the roll speed detector 54 of the fourth stand by the calculator 133, and the control V is supplied to the roll driving device 43 of the third stand. With this output V;,', the roll driving device 43 of the third stand controls the roll speed of the third stand without changing the total tension T between the third stand and the fourth stand. In this case, the roll speeds of the second stand and the first stand must be changed, but since the roll speed of the second stand is so controlled automatically that the total tension T between the second stand and the third stand is not changed, and also the roll speed of the first stand is so controlled automatically that the total tension T between the first stand and the second stand is not changed, and no effect appears thereby.

When the gauge altering point A reaches the fourth stand, and the output signal of the detecting device 84 for detecting the gauge altering point of the fourth stand begins to be generated, the gate circuit 104 is opened by the signal, the gauge h, of the fourth stand in the new schedule is received by the calculator 110 for the roll gap, and the control m, is calculated. With this control m the driving device 14 for roll gap operates the screw-down device 24, so that the roll gap of the fourth stand is altered to the new roll gap 8,.

When this alteration begins, the output V, of the roll speed calculator 134 of the fourth stand is calculated so that the total tension T between the fourth stand and the fifth stand is maintained constant as in the preceding stands. With this output V,, the roll driving device 45 is operated, and the roll speed of the fourth stand is controlled so that the total tension T is not changed. What has to be controlled is the roll speed control of the third stand, the second stand and the first stand, but as explained previously, since each of the stands is so controlled that no change is produced in the total tension T between each of the stands, the required control will be provided.

When the gauge alteration of the fourth stand is terminated, and the gauge altering point A reaches the fifth stand, the gate circuit 105 is opened by the output signal of the detecting device 85 for detecting the gauge altering point of the fifth stand, the control is effected by the new schedule, so that it is possible to obtain a rolled material which has different gauges on both sides of the gauge altering point A and the point B whre the alteration has terminated. Also, with this control, it is possible to reduce the off-gauge portion from A to B.

In the embodiment shown in FIGS. 3a-3c, the control is effected by carrying the roll speed of the stand preceding the stand in which the altering point has been bitten so as to prevent the variation of tension to the stand following the stand where the gauge altering point has already been bitten. Contrary to this, it is of course possible that the same control can be effected by changing the roll speed of the stand following the stand where the gauge altering point has been bitten.

While we have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to a person skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are obvious to one of ordinary skill in the art.

What is claimed is:

1. Thickness control apparatus for a rolling mill comprising at least two sets of rolling stands arranged so that rolling material will pass therethrough in series, transition detecting means at each rolling stand for detecting the presence of a gauge altering point in the rolling material at each stand, thickness calculating means associated with each of said rolling stands for calculating the amount of roll gap alteration required at each rolling stand in response to the transition detecting means at each rolling stand, means responsive to said thickness calculating means for changing the roll gaps at each rolling stand, and speed control means for controlling the roll speed of the one rolling stand at which the gauge altering point is detected to maintain the total tension in the rolling material between said one rolling stand and the immediately following stand at a previously predetermined value, in order to protect against a change in said predetermined value in response to a transient change in the delivery thickness of the material to said immediately following stand caused by alteration of the roll gap of said one stand.

2. Thickness control apparatus as defined in Claim 1, wherein said transition detecting means at the first rolling stand includes first means for integrating the roll speed of the first stand from the time of detection of said gauge altering point at said first stand and second means for generating a control signal when the integrated value from said first means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.

3. Thickness control apparatus as defined in Claim 2, wherein said transition detecting means at each rolling stand subsequent to said first rolling stand includes third means responsive to a control signal from the transition detecting means of the preceding rolling stand for integrating the roll speed of the respective stand and fourth means for generating a control signal when the integrated value from said third means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.

4. Thickness control apparatus as defined in Claim 3, wherein said transition detecting means at the first rolling stand further includes detecting means for detecting the actual presence of the gauge altering point at the first rolling stand for actuating said first means.

5. Thickness control apparatus as defined in Claim 1, wherein said means for changing the roll gap comprises rolling schedule instructing means for setting the roll speed for each of said stands and providing at least two different sets of roll thickness signals for each stand, calculating means for calculating the roll gap for each stand corresponding to the output of said instructing means, and gating means responsive to respective transition detecting means for selectively applying said roll thickness signals from said instructing means to said calculating means.

6. Thickness control apparatus as defined in Claim 5, wherein said transition detecting means at the first rolling stand includes first means for integrating the roll speed of the first stand from the time of detection of said gauge altering point at said first stand and second means for generating a control signal when the integrated value from said first means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.

7. Thickness control apparatus as defined in Claim 6, wherein said transition detecting means at each rolling stand subsequent to said first rolling stand includes third means responsive to a control signal from the transition detecting means of the preceding rolling stand for integrating the roll speed of the respective stand and fourth means for generating a control signal when the integrated value from said third means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.

8. Thickness control apparatus as defined in claim 1, wherein said speed control means further includes means responsive to said transition detecting means at a following stand for varying the roll speed at the immediately preceding stand in accordance with a predetermined relationship when said gauge altering point reaches said following stand and said means for changing the roll gaps adjusts the roll gap of said following stand, so as to prevent a change in tension in the material between said following stand and the immediately preceding stand.

9. Thickness control apparatus as defined in Claim 8, wherein said means for changing the roll gap comprises rolling schedule instructing means for setting the roll speed for each of said stands and providing at least two different sets of roll thickness signals for each stand, calculating means for calculating the roll gap for each stand corresponding to the output of said instructing means, and gating means responsive to respective transition detecting means for selectively applying said roll thickness signals from said instructing means to said calculating means.

10. Thickness control apparatus as defined in Claim 8, wherein said transition detecting means at the first rolling stand includes first means for integrating the roll speed of the first stand from the time of detection of the gauge altering point at said first stand and second means for generating a control signal when the integrated value from said first means has reached a predetermined value, indicating that the gauge altering point has reached the next stand, and wherein said transition detecting means at each rolling stand subsequent to said first rolling stand includes third means responsive to a control signal from the transition detecting means of the preceding rolling stand for integrating the roll speed of the respective stand and fourth means for generating a control signal when the integrated value from said third means has reached a predetermined value, indicating that the gauge altering point has reached the next stand ll. Thickness control apparatus as defined in claim 1, wherein said speed control means further includes means responsive to the detection of the presence of said guage altering point at one of the following stands in the series arrangement of successive stands by said transition detecting means for varying the roll speed at each of the preceding stands in accordance with a predetermined relationship for preventing a change in tension in the material between said one following stand and said immediately preceding stand as well as preventing a change in tension of the material between each of the other preceding stands. 

1. Thickness control apparatus for a rolling mill comprising at least two sets of rolling stands arranged so that rolling material will pass therethrough in series, transition detecting means at each rolling stand for detecting the presence of a gauge altering point in the rolling material at each stand, thickness calculating means associated with each of said rolling stands for calculating the amount of roll gap alteration required at each rolling stand in response to the transition detecting means at each rolling stand, means responsive to said thickness calculating means for changing the roll gaps at each rolling stand, and speed control means for controlling the roll speed of the one rolling stand at which the gauge altering point is detected to maintain the total tension in the rolling material between said one rolling stand and the immediately following stand at a previously predetermined value, in order to protect against a change in said predetermined value in response to a transient change in the delivery thickness of the material to said immediately following stand caused by alteration of the roll gap of said one stand.
 2. Thickness control apparatus as defined in Claim 1, wherein said transition detecting means at the first rolling stand includes first means for integrating the roll speed of the first stand from the time of detection of said gauge altering point at said first stand and second means for generating a control signal when the integrated value from said first means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.
 3. Thickness control apparatus as defined in Claim 2, wherein said transition detecting means at each rolling stand subsequent to said first rolling stand includes third means responsive to a control signal from the transition detecting means of the preceding rolling stand for integrating the roll speed of the respective stand and fourth means for generating a control signal when the integrated value from said third means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.
 4. Thickness control apparatus as defined in Claim 3, wherein said transition detecting means at the first rolling stand further includes detecting means for detecting the actual presence of the gauge altering point at the first rolling stand for actuating said first means.
 5. Thickness control apparatus as defined in Claim 1, wherein said means for changing the roll gap comprises rolling schedule instructing means for setting the roll speed for each of said stands and providing at least two different sets of roll thickness signals for each stand, calculating means for calculating the roll gap for each stand corresponding to the output of said instructing means, and gating means responsive to respective transition detecting means for selectively applying said roll thickness signals from said instructing means to said calculating means.
 6. Thickness control apparatus as defined in Claim 5, wherein said transition detecting means at the first rolling stand includes first means for integrating the roll speed of the first stand from thE time of detection of said gauge altering point at said first stand and second means for generating a control signal when the integrated value from said first means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.
 7. Thickness control apparatus as defined in Claim 6, wherein said transition detecting means at each rolling stand subsequent to said first rolling stand includes third means responsive to a control signal from the transition detecting means of the preceding rolling stand for integrating the roll speed of the respective stand and fourth means for generating a control signal when the integrated value from said third means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.
 8. Thickness control apparatus as defined in claim 1, wherein said speed control means further includes means responsive to said transition detecting means at a following stand for varying the roll speed at the immediately preceding stand in accordance with a predetermined relationship when said gauge altering point reaches said following stand and said means for changing the roll gaps adjusts the roll gap of said following stand, so as to prevent a change in tension in the material between said following stand and the immediately preceding stand.
 9. Thickness control apparatus as defined in Claim 8, wherein said means for changing the roll gap comprises rolling schedule instructing means for setting the roll speed for each of said stands and providing at least two different sets of roll thickness signals for each stand, calculating means for calculating the roll gap for each stand corresponding to the output of said instructing means, and gating means responsive to respective transition detecting means for selectively applying said roll thickness signals from said instructing means to said calculating means.
 10. Thickness control apparatus as defined in Claim 8, wherein said transition detecting means at the first rolling stand includes first means for integrating the roll speed of the first stand from the time of detection of the gauge altering point at said first stand and second means for generating a control signal when the integrated value from said first means has reached a predetermined value, indicating that the gauge altering point has reached the next stand, and wherein said transition detecting means at each rolling stand subsequent to said first rolling stand includes third means responsive to a control signal from the transition detecting means of the preceding rolling stand for integrating the roll speed of the respective stand and fourth means for generating a control signal when the integrated value from said third means has reached a predetermined value, indicating that the gauge altering point has reached the next stand.
 11. Thickness control apparatus as defined in claim 1, wherein said speed control means further includes means responsive to the detection of the presence of said guage altering point at one of the following stands in the series arrangement of successive stands by said transition detecting means for varying the roll speed at each of the preceding stands in accordance with a predetermined relationship for preventing a change in tension in the material between said one following stand and said immediately preceding stand as well as preventing a change in tension of the material between each of the other preceding stands. 